Which two events trigger an IS-IS LSP to be sent to a neighboring IS? (Choose two.)

A.
When a new IS-IS neighbor is detected.

B.
When the cost of a link to an existing IS-IS neighbor has changed.

C.
When a CSNP requests missing information.

D.
When a device does not receive an expected IIH PDU.

Explanation:
Troubleshooting IS-IS Adjacencies

The command show clns is-neighbors displays the IS-IS neighbor table. The entire table is displayed by default, or you can specify a particular interface. From this table, you can observe whether all expected neighbors are present and whether they are the correct type. For more information, such as the area addresses and IP addresses associated with each neighbor and the uptime of each neighbor, use the show clns is-neighbors detail command.

When examining adjacencies, consider the following:

* Are the router levels configured correctly? L1 routers can establish adjacencies only with L1 and L1/L2 routers, and L2 routers can establish adjacencies only with L2 and L1/L2 routers.
* Are Hellos being sent from both neighbors? Are the Hellos the correct level, and do they contain the correct parameters? The command debug isis adj-packets is useful for observing Hellos.
* If authentication is being used, are the passwords and authentication mode the same between neighbors? Remember that area (level 1) and domain (level 2) authentication do not regulate adjacencies, only the exchange of LSPs.
* Are any access lists blocking IS-IS or CLNS?